Answer:
Who keeps the ocean clean?
I am a word. I become longer when the third letter is removed.
You may enter, but you may not come in. I have space, but no room, I have keys, but open no lock. What am I?
What can travel around the world while staying in a corner?
What has a neck but no head?
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.